Condensation of alkoxysilanes in alcoholic media: II. Oligomerization of aminopropylmethyldiethoxysilane and co-oligomerization with dimethyldiethoxysilane

Abstract : In the context of the preservation of cultural heritage, the treatment of paper by an aminoalkylalkoxysilane, or its mixturewith dimethyldiethoxysilane (DMDES), gave encouraging results. The condensation experiments presented here, carried out inalcoholmedium using aminopropylmethyldiethoxysilane (AMDES) alone or with DMDES,were followed using 1HNMR, 29SiNMRand matrix-assisted laser desorption ionization time-of-flight (MALDI TOF) spectroscopies. The aim was to determine whetherDMDES and AMDES could copolymerize under the conditions used. An exchange reaction was observed for AMDES in ethanolin the absence of water, under conditions where no exchange took place for DMDES. In methanol, this reaction proceededmuch more rapidly and the reactivity of methoxysilyl groups was higher than that of ethoxysilyl groups. In the same solvent, inthe presence of water, hydrolysis, cyclization and oligomerization were observed using NMR and MALDI TOF spectroscopies. Inethanol, a kinetic study of a mixture of DMDES and AMDES showed that the condensation of the two monomers proceeded atcomparables rates and MALDI-TOF analysis gave evidence that mixed oligomers were produced, containing from one to fourAMDES units. It was concluded that the co-oligomerization did not lead to a mixture of homo-oligomers, which would be dueto different hydrolysis and condensation kinetics, but induced the formation of co-oligomers.c 2010 Society of Chemical Industry